1. Field of the Invention
Embodiments of the present invention relate to the conversion control of a tiltrotor aircraft from a helicopter configuration to an airplane configuration and from an airplane configuration to a helicopter configuration. More particularly, embodiments of the present invention relate to systems and methods for automatically controlling the pylon positions of a tiltrotor aircraft based on a commanded airspeed, a commanded rate of change of airspeed, and whether the commanded airspeed is increasing or decreasing.
2. Background Information
A tiltrotor aircraft is generally an aircraft that can fly like a helicopter or like a propellered airplane, depending on the position of its rotors. A tiltrotor aircraft typically has at least one wing and at least two rotors located at either end of the wing. Each rotor is connected to a pod and each pod is, in turn, connected to the wing.
The pods are used to position each rotor relative to the wing. A pod that encloses one or more engines powering the rotor connected to the pod and positions the engine in addition to the rotor is called a nacelle. A pod that does not contain an engine powering the rotor connected to the pod is called a pylon. The term “pylon” is hereinafter used to refer to a pod, a nacelle, or a pylon.
A tiltrotor aircraft can be flown like a helicopter by generally positioning the pylons of the aircraft relative to the wing so that the rotors rotate about a generally vertical axis and in a horizontal plane. A tiltrotor can be flown like a propellered airplane by generally positioning the pylons of the aircraft so that the rotors rotate about a horizontal axis and in a vertical plane. The process of changing the position of the pylons of a tiltrotor aircraft between the vertical position (helicopter configuration) and the horizontal position (airplane configuration) or the horizontal position and the vertical position during flight is called conversion.
Conversion is typically a manual process on tiltrotor aircraft. The pilot controls the conversion process by using a pylon switch on a collective control grip or power control grip of the aircraft. This pylon switch has a center off position, a forward position for converting from helicopter to airplane configuration, and an aft position for converting from airplane to helicopter configuration. The pylon actuators are run at a specified speed while the pylon switch is held in either position by the pilot. In another configuration, the pylon switch includes a position for emergency rapid conversion back to a helicopter. In still another configuration, the pylons are driven to discrete preset positions when a pilot operates the pylon switch.
In view of the foregoing, it can be appreciated that a need exists for systems and methods that can automatically control the pylon positions of a tiltrotor aircraft during conversion.